New Geometries for Ring Resonator Sensing

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Abstract

This thesis presents a detailed study of complementary metal-oxide-semiconductor (CMOS) compatible silicon waveguide and ring resonator technologies. The project specifically focuses on a range of slotted ring resonator configurations comprised of rib-style waveguides. Single ring resonators and Mach-Zehnder interferometers with double rings and central drop port channels have been successfully characterised. Thermal tuning techniques using on-chip heaters were used to determine their sensitivities. A stringent signal cleaning method was also developed to remove systematic background noise. Analysing the transmission signals produced by the Mach-Zehnder interferometers with double rings and a central drop port, it was revealed that coupled resonator induced transparency (CRIT) is created along with Fano-type resonances when the resonant peaks of the two ring resonators are tuned to overlap. The tuning of these features revealed a 2.7 and 2-fold improvement in device sensitivity. A 3x3 transfer matrix model has been developed to simulate the behaviour of light travelling through this configuration. Modelling suggests that effective refractive index and relative phase are the key factors in determining this behaviour. When tuned to close proximity, a resonant ‘superstate’ is achieved in which a modified model is required. Applying the single ring resonators to biosensing applications, basic refractive index testing and a glucose sensing calibration were conducted. A polydimethylsiloxane (PDMS) based microfluidics system was also developed to improve the reliability of sensing and enable automation. Using silicon nitride ring resonators with inkjet-printed upconverting nanoparticles, it was found that the evanescent field of the rings could stimulate the upconversion process revealing visible spectrum emission around the rings.

Keyword(s)

Biosensor; Lab-on-a-chip; Optical Switch; Optical filter; Ring resonator; Silicon; Waveguide

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